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of the face above that elevation. The concrete slab will be thoroughly drained by a network of porous-concrete drain tile. The spillway channel floor is being covered with a reinforced concrete slab and the side lining covered with a layer of gunite, reinforced with steel mesh. Incident to the repairs, as described previously, the dam and spillway crest are being raised and the automatic operating mechanism for the spillway gates altered.

In order to unwater the foundation and gain access to the downstream toe of the dam, a tunnel has been constructed, connecting two of the power outlets and one irrigation outlet in the lower tier of conduits with the existing diversion tunnel below the concrete plug. A cofferdam is being constructed upstream from the old diversion tunnel outlet and water for irrigation demands will be diverted around the dam through this tunnel.

to the various parts of the work by chutes, dump cars, an auxiliary cableway, and a traveling derrick.

The sand-cement plant was located at the north abutment of the dam. The mill consisted of a rock crusher, a pair of sand rolls, a ball mill, and four tube mills. The plant had a capacity of 2,000 barrels of sand cement in a 24-hour period. After grinding, the sand cement was carried across the river by a 3-inch pipe pneumatic conveyor to the mixing plant. The sand-cement plant manufactured a total of 586,450 barrels of sand-cement. It was estimated that the savings effected by the use of the sand-cement over straight portland cement totaled approximately $300,000.

It is estimated that there are 3,000,000,000 feet of timber on the Boise River watershed above Arrowrock Dam. To provide a means for getting logs out of the reservoir, over the dam, and into the river again, a log conveyor was built at the south end of the dam. It was designed for a capacity of 60,000,000 feet of logs during a season lasting from May 1 to July 15.

The conveyor consists of a “lift” by which the logs are raised from the reservoir to a log deck by cable loops; live rolls across the dam; an endless chain chute 390 feet long on a 62.5 percent grade; and a gravity chute 245 feet long on a 32 percent grade. The structures are built of reinforced concrete and structural steel.

Construction of the log conveyor was started in March 1915, and finished in November 1915, with the exception of placing a smal amount of machinery, which was completed in the early part of 1916.

The principal quantities involved in the construction of the log conveyor were 8,265 cubic yards of excavation, 2,134 cubic yards of concrete, 84,060 pounds of reinforcement steel, 300,390 pounds of machinery and structural steel, and 200 linear feet of tunnel.


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The cost of the original construction of the dam, and appurtenant works was $4,796,489, subdivided as follows: Preliminary surveys and examinations ......... $8,720.61 Preliminary and general work (including foundation

testing, net cost of railroad, etc.) ............ 177,172.37 Right-of-way ....................

70,570.86 Water rights...


76,486.72 Telephone system ......

.... 9,675.20 Power plant and transmission lines . .

195,305.00 Dam (including construction camp, diversion works, pumping, etc.) ........

3,611,048.51 Log conveyor and crane ..

63,560.64 Power outlets ..........

... 19,451.36 Spillway .........

531,136.51 Bridge over spillway..

3,749.04 Buildings (permanent) ...


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During the 20 years since the dam was built, the downstream face of the dam, the spillway channel lining, and other exposed surfaces which were made of the sandcement concrete, have suffered some disintegration. This has been due, primarily, to the fact that the sand-cement concrete was very porous and absorbed water freely, resulting in rapid spalling with alternate freezing and thawing. It became apparent as early as 1927 that means had to be taken to protect the concrete surfaces from the action of water.

In 1935, $600,000 was made available for making repairs to the dam and spillway. Contract for construction was awarded to T. E. Connelly, Inc., of San Francisco, Calif., on January 10, 1936.

The repairs to the dam include an 18-inch reinforced concrete slab on the downstream face below elevation 3197.75, and a gunite covering on the remaining portion

Inasmuch as the work on the original dam was done by force account, accurate subdivisions for determining unit prices could not be made. Approximate unit prices, as determined for the major items of construction, were as follows: Item

Unit price Diversion tunnel excavation ........... $6.20 per cubic yard Excavation for dam (all classes) ........ $1.45 per cubic yard Excavation for spillway ............. $0.75 per cubic yard Concrete in dam ................. $4.00 per cubic yard Reinforced concrete in spillway . . . . . . . . . $7.50 per cubic yard Structural-steel spillway gates and outlet con

duits ...................... $0.08 per pound Construction camp (construction and mainte

nance) ..................... $225,000 Diversion works (complete) ........... $350,000 Unwatering dam foundation .......... $45,000

The work on the alterations to the dam and spillway, as of December 1, 1936, is about 40 percent complete. Approximately $235,000 of the $600,000 estimated to complete the project were expended up to that date.


Bache, Reve. Government Runs Railroad to Build Biggest

Dam. Technical World, May 1912, vol. 17, pp. 311-314. Clawson, R. R. Messhouse Management at the Arrowrock Dam. Engineering News, June 24, 1915, vol. 73,

pp. 1201-1203. Cunningham, M. F. The Arrowrock Dam. Western

Engineering, November 1915, vol. 6, p. 192 (see also

Pacific Builder and Engineer, April 1916, vol. 21, p. 194). Davis, A. P. Irrigation Works Constructed by the United

States Government. John Wiley & Sons, New York. Davis, A. P., and Wilson, H. M. Irrigation Engineering.

John Wiley & Sons, New York. Doll, M. G. The Arrowrock Dam. Mine and Quarry,

August 1913, vol. 7, p. 753 (see also Engineering Record,

September 6, 1913, vol. 68, pp. 265-267). Ensign, O. H.: Hydroelectric Plant for Construction Work (Boise Plant).

Engineering Record, Aug. 24, 1912, vol. 66, pp. 209– 211. Large Balanced Valves for Reservoir Outlets. Engineer

ing Record, July 11, 1914, vol. 70, p. 53. Gaylord, J. M. How Water is Controlled at the Arrowrock

Dam. Rec. Record, August 1916, vol. 7, pp. 359–360 (see also Engineering Record, Sept. 30, 1916, vol. 74,

p. 409). Hanna, F. W. Progress on Arrowrock Dam. Engineering

Record, Mar. 7, 1914, vol. 69, p. 272. Mayhew, A. B. Construction Camp at Arrowrock Dam.

Engineering Record, Aug. 2, 1913, vol. 68, pp. 116-118.

Paul, C. H.:
Diversion Works for Arrowrock Dam. Engineering

Record, Apr. 6, 1912, vol. 65, p. 368 (see also Engineer-
ing News, June 6, 1912, vol. 67, pp. 1061-1065; Eng. &
Cont., Aug. 21, 1912, vol. 38, p. 218; Engineering News,
Jan. 16, 1913, vol. 69, pp. 118-120; Engineering Record,

Feb. 22, 1913, vol. 67, pp. 214–215).
Sand Cement as Used by the United States Reclamation

Service (Including costs). Engineering News, Mar. 20, 1913, vol. 69, pp. 562–563. (See also Engineering Record, Mar. 29, 1913, vol. 67, p. 343; Eng. & Cont., May 21, 1913, vol. 39, p. 571; Trans. Am. Soc. C. E.,

vol. 76, p. 560.) Excavation for Arrowrock Dam, Idaho. Engineering

News, July 17, 1913, vol. 70, pp. 93–100. Excavation for Arrowrock Dam, Idaho. Water Power

Chronicle, September 1913, vol. 2, p. 139. Progress on the Arrowrock Dam. Engineering News,

June 11, 1914, vol. 71, pp. 1286–1288. Large Balanced Valves. Engineering Record, July 11,

1914, vol. 70, p. 53. (Short editorial, p. 31.) Concreting the Arrowrock Dam. Engineering Record,

Aug. 8, 1914, vol. 70, pp. 152–153. Discussion of Grouting Arrowrock Dam. Trans. Am.

Soc. C. E., 1915, vol. 78, p. 535. Install Huge Balanced Valves at Arrowrock Dam.

Engineering Record, Feb. 13, 1915, vol. 71, p. 208. Log Handling Equipment at Arrowrock Dam. Engineer

ing News, July 29, 1915, vol. 74, pp. 200–201. Paul, C. H. and Mayhew, A. B. Temperature Changes in Mass Concrete (Diagrams) (Discussion by A. J. Wiley). Trans. Am. Soc. C. E., May 5, 1915, vol. 79, pp. 12251267. (See also Engineering Record, June 5, 1915, vol. 71, p. 710; Engineering News, Nov. 11, 1915, vol. 74, p. 923; Engineering Record, Nov. 20, 1915, vol. 72, p. 624.) Most of the reservoir basin including that portion near the dam is in prebasaltic tuff which is practically impervious. The upper end of the basin, where the water is comparatively shallow, is in tight formations of conglomerate, sandstone, shale, and tuff. The portion near the mouth of Dry Creek is in Columbia River basalt, which constitutes the only place where leakage might occur. However, geological opinions indicate that no serious leakage is to be expected.




OWYHEE DAM is located on the Owyhee River 21 miles southwest of Nyssa, Oreg., and about 50 miles due west of Boise, Idaho. It was planned for both diversion and storage purposes, and was built under a contract awarded to the General Construction Co. of Seattle, Wash.

The Owyhee project was authorized by Congress in 1924. Preliminary construction work on the dam was begun in 1928, and the dam was completed in October 1932. The canal system which serves 92,000 acres is now nearing completion. The justification for the project was the relief of a large number of existing irrigation districts, in a high state of cultivation using water pumped from rivers. The construction of Owyhee project permits the use of a cheaper gravity supply and at the same time brings into cultivation additional lands not previously irrigated.

Owyhee Dam raises the water 315 feet above the original river level to the maximum reservoir surface elevation of 2,670. The crest of the dam is 417 feet above the foundation in the river section, and 530 feet above the lowest concrete in the fault zone cut-off, making it the world's tallest at the time it was completed. The dam regulates and controls the Owyhee River waters for diversion through the main canal tunnel no. 1 and the distribution system for the irrigation of land in eastern Oregon and western Idaho, and for supplying supplemental water to 13,690 acres under a Warren Act contract with the Owyhee Ditch Co.

DAM SITE The dam site is located at a place where the Owyhee River flows through a box canyon. Test holes show the foundation material to consist of sand, gravel, cobbles, and boulders to a maximum depth of 60 feet, below which rhyolite is found. The rhyolite extends to a depth of 170 to 215 feet below the water surface of the stream and is bedded on pitchstone agglomerate. All the geological and engineering opinions agreed that the foundation rock was suitable for the construction of the dam.

The most serious flaw in the rock is a shattered zone or fault crossing the dam site at about the center of the canyon. This shattered zone was first disclosed by core drilling and later by an open test pit located about 1,450 feet downstream from the dam site, where the fault leaves the canyon. During the foundation excavation, the seam was found to vary in width from about 12 to 20 feet, and to reach to depths of from 120 to 150 feet below elevation 2,300, all of which zone was removed across the full width of the dam, replaced with concrete and pressure grouted.

THE DAM Owyhee Dam is a concrete arch-gravity structure, with about three-fourths of the water load carried by arch action and one-fourth carried by gravity action. The radius of the upstream face at the top is 500 feet and both faces are concentric. The top thickness is 30 feet and the maximum bottom thickness, 265 feet. The upstream face is vertical for the top 75 feet and below this has a batter of 0.05 to 1. The downstream face is generally on a slope of 0.626 to 1. A gravity tangent, 210 feet long, was built at the right. abutment. The arch section is 600 feet long at the crest.

Before adopting the arch-gravity type of dam preliminary designs and estimates were prepared for five different types,


Owyhee Reservoir is 52 miles long with a total storage capacity of 1,120,000 acre-feet, including 405,000 acre-feet of dead storage. The drainage area above the reservoir is about 11,000 square miles, of which part lies in Nevada, including the headwaters of the Owyhee River and the South Fork of the Owyhee River. The other parts of the drainage area lie in southwestern Idaho and the southeast corner of Oregon. The reservoir filled for the first time in April 1936.

The average annual run-off is about 900,000 acre-feet. The maximum recorded flow occurred during 1891-92, amounting to 2,300,000 acre-feet. The minimum recorded annual flow was 153,000 acre-feet in 1931. Variations in stream flow of from 100 second-feet to 23,200 second-feet have been recorded.

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including a light arch section, an intermediate arch section, a heavy arch section (arch-gravity type), a straight gravity section, and a slightly curved gravity section. In all design studies, uplift pressures were assumed to act over the whole area of the base, varying from full hydrostatic pressure at the upstream face to one-half hydrostatic pressure at the drainage wells; then diminishing uniformly to zero or tailwater pressure at the downstream face.

Radial contraction joints were provided at 50-foot intervals along the dam. The joints were provided with vertical keyways, 9 inches deep by 3 feet wide, on 3-foot centers. Copper expansion sealing strips, consisting of 20-gage soft copper sheets bent to the shape of a T with double stem, were placed 12 inches from the upstream and downstream faces of the dam, and around all gallery openings. At each 100-foot level a horizontal strip connects the upstream

and downstream copper expansion strips, forming a watertight diaphragm. A system of pipes and fittings was embedded in each joint, for the purpose of grouting after the mass concrete cooled to below the mean annual temperature of 52° F.

All gate installations, drainage wells, the elevator shaft, inspection shafts, and transverse and radial inspection galleries are accessible through spiral stairway shafts and through 5- by 7-foot circumferential, inclined and horizontal drainage galleries. An entrance adit at elevation 2,377.8 is located in the left abutment, about 200 feet below the dam; and access to the galleries is provided through a 6- by 8-foot tunnel excavated in the foundation rock. The tunnel portal structure is of concrete and is provided with sheet metal doors and a structural steel gate.

The right abutment entrance adit to the dam is located at

closure, utilizing headwall grooves. Keyways were provided upstream from the spillway shaft for final closure by means of a concrete plug. The tunnel plug was provided with an embedded pipe grouting system, through which the tunnel plug was ultimately grouted during the early summer of 1934, about 20 months after the dam was completed.

Studies of the capacity curve of the diversion tunnel as compared with the maximum river discharge indicated the necessity for a height of cofferdam of about 60 to 75 feet.


station 8+75, elevation 2,661.25, and is provided with sheet metal doors. A 23-step steel stairway, with 2-inch pipe railing on either side, runs parallel with the downstream face of the dam from the adit to the elevation of the roadway.

The left abutment entrance to the galleries is through a 9-foot inside diameter concrete turret house, located at station 0+75 near the downstream parapet wall. A 5- by 7foot concrete lined connecting tunnel, excavated in the foundation rock beneath the roadway pavement beyond the southwest end of the dam, connects the inspection galleries of the dam with a spiral stairway shaft located directly beneath the floor of the turret house.

All galleries and shafts in the dam provide drainage facilities, the seepage being ultimately focalized in an outfall system near the base of the dam.

Drain holes have been drilled in the abutments and base of the dam from the galleries and spiral stairway shafts of the drainage gallery. Diamond drilling followed concrete placement as rapidly as the removal of gallery forms permitted, and was completed in May 1932.

An elaborate system of 374-inch metal drain pipes was embedded throughout the dam, and all drainage collected throughout the drainage system is ultimately collected and discharged below tailwater elevation by three 24-inch drain tiles.

A volume of 536,471 cubic yards of concrete was involved in the dam and appurtenant works. The quantities included in the various features are tabulated as follows:

The spillway consists of a reinforced concrete lined vertical shaft connecting with the diversion tunnel through a 50foot radius, 90-degree bend, at a point about 235 feet below the tunnel intake. The diameter of the shaft changes through a 156-foot transition from 52.33 feet at the inside lip of the crest structure to 22.6 feet at elevation 2,513.

The spillway shaft is controlled by a 60- by 12-foot spillway ring gate, operating in an annular pressure chamber formed in the crest structure. The ring gate is a floating type crest, similar in operation to the drum gate, but designed with’much better hydraulic conditions for flow into a vertical spillway shaft. The gate is of structural-steel construction embodying 12 shop-riveted segments, which were riveted together in the field. The operation of the ring gate is controlled by a needle-type valve in the same manner as in recent drum-gate installations. The use of the ring gate effected a material saving in cost as compared with usual drum-gate installations.

The designed discharge capacity of the spillway is 40,000 second-feet with the gate down, crest at elevation 2,658, and the normal water surface in the reservoir with the gate up, is at elevation 2,670. A model test of the spillway structure was made in the hydraulic laboratory to study the behavior of the ring gate and its effect upon the flow through the vertical transition section at the top of the vertical shaft.

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The cost of the concrete in the dam and appurtenant works represented more than 50 percent of the total expenditures for the storage unit of the Owyhee project. The selection of aggregates, determination of the most suitable and economical mix, control of placing, and tests of resuits constituted an important feature of the engineering work.


Gate installations in the dam include sluice-gate outlets at elevation 2,370, needle valve outlets at elevation 2,470, and power penstock outlets at elevation 2,570.

Sluice gate outlets consist of three conduits, each conduit leading to two 4- by 5-foot cast-iron sluice gates arranged in tandem. The gates are operated hydraulically against a maximum reservoir head of 300 feet. The upper 50 feet of the outlets are lined with 60-inch cast-iron conduit linings, while the lower 134 feet consist of 60-inch unreinforced barrels cored in the mass concrete. The shape of the outlet conduits changes, just beyond the gates, from a 4- by 5-foot rectangle, to a 5-foot circular section, through a 9-foot transition. Vacuum is prevented below the gates at partial gate openings by 8-inch air vent pipes, extending from behind

The designs provided a 22.6-foot diameter circular tunnel, concrete lined and pressure grouted, 1,005 feet long, for diversion of the river during construction. The tunnel was located through the right abutment and the greater part of the tunnel was later utilized for the permanent spillway. The tunnel intake was designed with provision for temporary

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